Can anyone cite any credible study, research, data, etc., which substantiates the opinion it is unsafe to use a plug to repair a motorcycle tire? The reason behind this question is one of my co-workers was turned away from motorcycle training, and the reason cited by the instructor was because of a plug in the rear tire. My co-worker bought the tire almost three years ago, and within a few days of purchase he picked up a nail in the meat of the tire, just off center. He had a service department plug the tire, and he has ridden over 1500 miles on the tire since the repair. He has never had a problem with the tire, and was confused as to why this was assessed as unsafe by the instructor.

I have since talked to a local service department, Michelin USA corporate (the tire in question is a Michelin Pilot Power), the Rubber Manufacturers Association (oversees tire manufacturers in the U.S.), and the National Highway Traffic Safety Administration, and I have online researched other local/state/national regulations and safety inspection standards, and I can find nothing at all to explain if it is actually safe or unsafe to use a plug to repair a motorcycle tire (in the meat of the tread, not in the sidewall). The local service dept. and Michelin said it was very unsafe and not recommended, but they could offer no explanation why it is so unsafe, except in extremely vague, ambiguous terms. The remaining associations/agencies had no recommendations at all. Frankly I distrust the first two because I believe they are financially motivated ("we can't plug that tire, but we'll happily sell you a new one") and/or they are more concerned about liability lawsuits.

Well just think about the centrifugal force on the tire. With all that force at speed the likely hood of the plug coming out is pretty high. A plug i wouldn't trust, a patch from the inside of the tire i would trust a little bit more, but me personally i would just buy a new tire. We rely on only two wheels i wouldn't want one failing at speed. Why even take that risk for a couple hundred dollars? My safety is a little more important. You spend hundreds on all the safety gear to ride why ride on a bum tire? Just my .02.

Well just think about the centrifugal force on the tire. With all that force at speed the likely hood of the plug coming out is pretty high.

Tires are essentially layers of different materials held together by chemical and heat curing. Do you worry your tires will fly apart due to centrifugal force? Of course not, because it is proven through manufacturer research and also actual use by consumers this is unfounded fear. Catastrophic failures do still happen, but they are sufficiently rare we are not scared away.

I certainly follow the point you are making, but this idea is purely speculative, since no one has proved it to be true (that I can find). I find it strange people are so willing to accept it as completely true with no supporting evidence. If we are so risk averse, why are we riding motorcycles in the first place?

In the end, my point is not that I think it is a great idea to ride around on repaired tires. My point is no one (again that I can find) has actually studied the idea and determined it to be safe or not. Until someone does, and I doubt they ever will (due to expense to private researchers, and fear of lawsuits by the manufacturers), we continue to use fear and speculation to drive opinion on whether a repair is reliable and safe.

On the Dunlop website it says it is safe to plug a tire for speeds no faster than 75 mph. When i say at speeds i am talking track speeds which most of us ride. I also ride faster than 75 mph on the street at times so me personally i would not plug a tire. I am sure the Dunlop guy will be around at some point to correct me. But either way i would still just buy a new tire so i wouldn't have to find out the hard way.

On the Dunlop website it says it is safe to plug a tire for speeds no faster than 75 mph. When i say at speeds i am talking track speeds which most of us ride. I also ride faster than 75 mph on the street at times so me personally i would not plug a tire. I am sure the Dunlop guy will be around at some point to correct me. But either way i would still just buy a new tire so i wouldn't have to find out the hard way.

Thanks for that comment about the Dunlop website. I had not previously checked out their site, so my manufacturers comments were limited to those provided by Michelin.

As regards track use, I am inclined to side completely with you on this one. I still would like to see something more definitive on the subject, but on the whole I suspect track use would be asking a lot more than is reasonable for a repaired tire.

Shifting topics slightly, I'm somewhat surprised to see you comment you at times ride at 75mph or more on the street. When someone says "street" I usually take that to mean local roads (posted speed limits in roughly the 25-45mph range). Did you mean highway riding or "streets"?

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Posted 21 April 2011 - 01:45 PM

Can anyone cite any credible study, research, data, etc., which substantiates the opinion it is unsafe to use a plug to repair a motorcycle tire? The reason behind this question is one of my co-workers was turned away from motorcycle training, and the reason cited by the instructor was because of a plug in the rear tire. My co-worker bought the tire almost three years ago, and within a few days of purchase he picked up a nail in the meat of the tire, just off center. He had a service department plug the tire, and he has ridden over 1500 miles on the tire since the repair. He has never had a problem with the tire, and was confused as to why this was assessed as unsafe by the instructor.

I have since talked to a local service department, Michelin USA corporate (the tire in question is a Michelin Pilot Power), the Rubber Manufacturers Association (oversees tire manufacturers in the U.S.), and the National Highway Traffic Safety Administration, and I have online researched other local/state/national regulations and safety inspection standards, and I can find nothing at all to explain if it is actually safe or unsafe to use a plug to repair a motorcycle tire (in the meat of the tread, not in the sidewall). The local service dept. and Michelin said it was very unsafe and not recommended, but they could offer no explanation why it is so unsafe, except in extremely vague, ambiguous terms. The remaining associations/agencies had no recommendations at all. Frankly I distrust the first two because I believe they are financially motivated ("we can't plug that tire, but we'll happily sell you a new one") and/or they are more concerned about liability lawsuits.

All Lawyers aside, here is my answer:

It is not safe to use a plugged tire on the track. end of story.

Here is why. Its all about temperature and contamination.

When the tire is punctured, the carcus get exposed to air and contamination. that hole, even if plugged, now generates more heat, more flex and the layers now are trying to separate from each other. As the layers start to slightly separate they get more contamination between the layer and thus more heat and more separation. This gets worse and worse the faster you go and the more you use it. You will see separation and/or bubble and/or overheating from the hole outward. If you go slow (75 or less) this process does not happen. Its the extreme heat and flex of the racetrack that makes this come about.

Big rider, on a big bike, that rides fast in the hot dessert, you would expect the same issues as with the track.